The overall goal of this research is to better understand the mechanisms underlying pattern formation during development and regeneration in the coelenterate, hydra. Hydra has a simple body plan and is easy to manipulate in a variety of ways. For this reason the animal is a good model system is which to study the processes of pattern formation and pattern regulation. The central issue is what controls head formation at the apical end of the animal and foot formation at the lower end. From numerous grafting experiments it has been demonstrated that developmental gradients of head and foot activation and inhibition exist in the animal. More recently, the dynamics of these gradients have been worked out, and a theoretical model based on diffusible substances has been proposed to describe patterning in hydra. This earlier work has all involved manipulation of the animal -grafting or excising tissue - followed by an analysis of structures formed several days later. To get more detailed information on the patterning processes, one would like to follow the dynamics of head and foot formation before morphology is evident. This can be done using monoclonal antibodies which label head or foot-specific antigens before the structures appear during the patterning processes. The monoclonal antibody CP8 is being used to study the dynamics of head formation. The research in this proposal will continue investigating the patterning processes in hydra using CP8 and other position-specific antibodies by examining (1) the role tissue healing has in the early dynamics of head regeneration; (2) the relationship between the mechanisms which form the head field and subsequently proportion tissue into the head; (3) the effect of exogeneous head activator on the dynamics of head regeneration; 94) the de novo formation of heads following reaggregation of dissociated hydra tissue; (5) the embryogenesis of the head; (6) the interaction of the head an foot patterning processes during regeneration; (7) the effect of exogeneous head activator on these interactions; and (8) the fit between quantitative data derived from studying the dynamics of head formation and numerical (computer) simulations of head formation.